FIG. 1 is a perspective view of a known mower, typically referred to as a mid-mount Z type mower. The mid-mount Z mower of FIG. 1 includes a pair of rear drive wheels 43 each of which is driven by a hydro (hydrostatic or hydraulic) pump so that two pumps are provided, steering levers 15, 16, frame 17, cutter or mower deck assembly 12 below which the blades cut grass, operator seat 18 for a seated operator, gas tank 19, combustion engine 58 located behind the seat, and front caster wheels 37. The mower is a zero radius turning self-propelled power lawn mower, and includes first and second hydro pumps (not shown) for controlling first and second corresponding wheel motors (not shown), so that the first and second independently driven rear drive wheels 43 may be driven independently in order to conduct zero radius turns.
It is known to attach large grass collection systems to self-propelled lawn mowers. Some grass collection systems include a grass storage compartment located rearward of the seat and engine of the mower. Such grass collection systems can weigh as much as approximately two hundred pounds or more when holding grass. This significant added weight can be problematic, especially when the grass collection system is such that the grass is collected and/or stored rearwardly of the mower's rear drive wheels (e.g., the mower may “pop wheelies” during operation). In order to compensate for this added rearward weight, it is known in the art to add metal counterweights to the front of the mower so as to reduce the likelihood of the mower popping wheelies during normal mower operations.
Unfortunately, the use of such counterweights on the front of the mower to offset the grass collector weight is problematic in that it can shorten the useful life of the mower. In particular, the use of such counterweights can lead to premature failure of a mower's hydraulic system which is very expensive to repair. Mower hydraulic systems, including the hydro pumps which control the rear drive wheel motors, are made to operate in a satisfactory manner up to about 2,000 psi. However, when too much weight is placed on the front and rear of the mower, the psi level can reach up to about 3,000 to 5,000 psi during mowing operations; when this occurs the hydraulic system can start to leak internally and extreme heat can be generated. This causes the hydraulic oil to deteriorate and leads to a too low viscosity. These occurrences lead to premature failure of the hydraulic system and thus of the mower.
In view of the above, it will be apparent that there exists a need in the art for an improved way in which to compensate for significant amounts of weight which may be added to a rear portion of a mower such as via a grass collection system.